Exchange 2016 requires essentially the same RAM/CPU/IOPs per mailbox as Exchange 2013 but requires just a little more compute requirements.
Exchange 2016 only has a single role (MBX role) so the Exchange 2013 guidance needs to be followed for multi role servers.
See here for more information on these changes: http://blogs.technet.com/b/exchange/archive/2015/10/15/ask-the-perf-guy-sizing-exchange-2016-deployments.aspx